This invention pertains to the manufacture of flat-panel electronic displays and, more particularly, to the manufacture of AMLCD type, flat-panel displays assembled from arrays of tiles, while maintaining tolerances in three dimensions.
Images on electronic displays are derived from an array of small, picture elements known as pixels. In color displays, these pixels comprise three color elements that produce the primary colors, for example, red, blue and green (R, B and G). Usually arranged in rectangular arrays, these pixels can be characterized by a pixel pitch, P, a quantity that measures the spacing of pixels in one direction. A typical cathode ray tube (CRT) display used for computer applications has a pixel pitch of 0.3 mm. Computer monitor screens typically have a pixel array width:height ratio of 4:3. Consumer television displays now often have a ratio of 16:9. Typical, standardized arrays in computer displays are composed of 640xc3x97480 (VGA), 800xc3x97600 pixels (SVGA), 848xc3x97480 (wide VGA), 1024xc3x97768 pixels (XGA), or 1280xc3x97720 (HDTV).
Large displays can be constructed from a plurality of adjacent tiles, each having a single pixel or an array thereof. Such assembled tiled displays contain visually disturbing seams, resulting from the gaps between adjacent pixels on adjacent tiles. Such seams may incorporate interconnect, adhesives, seals, mechanical alignment means and other components resulting in optically visible discontinuities in displayed images. Some of these structures are described in the aforementioned U.S. Pat. No. 5,661,531. As a consequence, the image portrayed on seamed displays appears segmented and disjointed. Therefore, it is desirable to fabricate tiled, flat-panel displays which do not have noticeable or perceptible seams under the intended viewing conditions.
The pixel pitch in electronic displays must be set so that a continuous image is produced when the display is viewed at distances greater than the minimum viewing distance. For example, with a pixel pitch of P=0.3 mm, the minimum viewing distance is on the order of 1 m. Even though the minimum viewing distance increases in proportion to the pixel pitch, this distance still limits the pixel pitch for most computer and consumer displays. Since space for the tiling functions must be provided in spaces smaller in size compared to the pixel pitch, it is difficult to develop structures and methods for constructing tiled displays.
Flat-panel displays (FPDs) provide the best choice for constructing xe2x80x9cseamlessxe2x80x9d, tiled screens. Flat-panel displays include back lighted and self-lighted displays. Liquid crystal displays (LCDs) are the most common back lighted displays. Flat-panel displays depend on the micro fabrication of key components that carry the pixel patterns. Such micro fabrication techniques, however, are not viable for very large displays, generally greater than 20 inches diagonal, due to the fact that the manufacturing yield declines rapidly with increasing area of the display. Therefore, the inventors have determined that tiles with arrays of pixels can be micro fabricated and then assembled together to form a larger electronic display.
The present invention provides unique designs and methods for achieving such large monolithic or monolithic-like seamless, tiled panels for color or gray-scale displays. This invention particularly focuses on displays of the transparent, light valve type. In such displays, light from a uniform, back light source is transmitted through the display assembly and directly viewed from the front side of the display. The light valves control the amount of primary light rays transmitted through each of the color elements in the pixels. The viewer""s eyes merge the primary light from the pixels to form a continuous image at a sufficient viewing distance.
A large FPD made by tiling smaller LCD panels may exhibit visual seams at the boundary of the two adjacent tiles. Light will primarily flow through the seams or gaps between tiles. The design of the tiled FPD structures must substantially eliminate this light emanating from the seams. This is accomplished by using masks within the assembled structure but external to the individual tiles. These masks are effective in preventing light within a preferred (i.e., designed) angular range from reaching the seams. The incident light at or near the seams is collimated to within this preferred angle. The mask lines, which are placed in the dark spaces between pixels repeat, at every pixel.
However, because of a number of secondary processes, low-level light emanates from regions near the seam because of other mechanisms. The optical mechanisms which include reflection and light guiding must be controlled to ensure emanated light near the seams is kept to a minimum in order to achieve sufficient brightness and contrast. At the edges of adjacent tiles, the spaces between pixels on the same tile and the spaces between edge pixels on adjacent tiles may have different structures. Consequently, the presence of seams between the pixels at the edge of the tiles will affect both primary and secondary light rays, thus making the construction of seamless, tiled displays more difficult. The masks are only partially effective in eliminating these optical artifacts at the seams of the tiled, flat-panel displays.
The residual visible artifacts remaining at the seams require both light intensity and color-correction of the pixels neighboring the seams, and balance of color and light intensity from tile to tile. These corrective actions may be achieved by several approaches utilizing control and driving electronics and software. Some techniques for performing these corrections are disclosed in U.S. Pat. Nos. 5,668,569; 6,020,868; 6,115,092; 6,181,392; 6,184,952; 6,184,953; 6,188,454; 6,243,059; and 6,271,825, all of which are commonly assigned to the assignee of the present invention.
In addition to the optical and electronic correction means, the inventors have identified three design principles in assembling large-size, seamless, flat-panel displays that may be viewed as though they were single monolithic displays:
a) the pixel pitch on the view plane for the tiles must be matched to that of the pixel pitch on the view plane between the tiles within a predetermined critical set of tolerances;
b) the primary light paths through the light valves must not be substantially affected by the presence of the seam or any other structures or components used in the tile assembly; and
c) the interpixel gaps must be designed so that intratile and intertile pixel gaps, which have different physical structures, present approximately the same visual appearance to the viewer under both transmitted and reflected light.
This has largely been accomplished by applying the technology disclosed in U.S. Pat. No. 5,661,531 to fabricated, tiled AMLCD functional models. In addition, U.S. Pat. Nos. 6,133,969 and 6,097,455 feature methods for assembling arrays of AMLCD tiles into tiled, flat-panel displays having visually imperceptible seams between the tiles. However, design improvements are possible to increase the manufacturing yield and the optical performance of the tiled displays from their component tile parts. The present invention focuses on preferred processes for assembling the tiles into robust laminates between glass cover plates and back plates. The instant invention also provides tooling elements for implementing these processes and facilitating high throughput assembly of AMLCD tiles into FPDs.
Tiled FPDs require a high degree of location precision and alignment in all three orthogonal dimensions, X, Y, and Z, to appear monolithically, optically continuous, pixel-to-pixel, across seams between neighboring tiles. The means to achieve AMLCD tiled FPDs in this invention require referencing the tiles along the Z dimension with optically clear adhesive films of a preferred thickness. This thickness must accommodate both intratile and tile-to-tile thickness variations without unduly affecting either primary or secondary light rays in the seam regions.
The tiles are spaced by the-films between continuous, flat, optically clear cover and back plates preferably containing masks, and having closely matched indices of refraction. At the same time, the horizontal (x) and vertical (y) dimensions of the FPD tiles are maintained, locating the pixels across the seams with continuity in pitch and parallelism. This is accomplished through the use of unique tools and by the use of a carefully controlled process of applying polymer adhesive materials to encapsulate the tiles between cover and back plates.
An important part of the process is maintaining location of the tiles and cover and back plates to each other while they are being handled and transferred during the assembly operations. This is achieved by applying small polymer adhesive dots (typically acrylic), which may be cured with UV light. These polymer adhesive dots are located in the perimeter, outside the active viewing area of the FPD, prior to applying the full face adhesive films.
The full face adhesive films, either liquid or solid, or a combination thereof, are typically in the range of approximately 50 to 500 microns in thickness, and are preferably in the range of approximately 50-150 microns. The films are also optimized in viscosity for rapid lamination of the tiles to cover and back plates. The adhesive is thermally cured.
After the lamination process is completed to reach the desired thickness of the adhesive and the precision location of the glass plates, the polymer dots are cured with UV light to maintain the relative locations of the tiles and cover and back plates. The assemblies are then sufficiently robust for transfer operations in the process sequence.
The full face adhesive polymer is generally cured in an oven. The fully cured polymer is sufficiently compliant over the full face surfaces of the tiles so as not to stress the tiles or alter the cell gap of the liquid crystal display tiles or display panels.
The present invention provides an improved method for laminating the components of an AMLCD tiled display. In conventional laminating, forces are applied to the two parallel glass plates (i.e., the cover and back plates) separated by a liquid adhesive film. The two plates are squeezed together over their entire area forcing liquid laterally out from between the glass plates and tiles until the desired spacing or gap (filled with liquid adhesive) between the cover and back plates and the tiles is obtained. However, this process may require several hours to complete for large panels and, in addition the process is susceptible to trapping air bubbles in the adhesive. Consequently, the traditional process is not well suited for the mass production of large panels. The xe2x80x9cpseudoxe2x80x9d rolling-like lamination process of the present invention replaces the traditional lamination process and requires significantly less time.
It is therefore an object of the invention to provide a novel lamination process for assembling AMLCD tiles suitable for use in constructing large, tiled flat-panel displays.
It is another object of the invention to provide a lamination process in which a thin cover plate and a thin, flexible back plate are bent at a predetermined radius of curvature, and an initial single point of contact with full face adhesive is progressively increased in area, as the contact front is moved across the plates.
It is a further object of the invention to provide a tool and lamination process for bending the cover and back plates at a predetermined radius of curvature and for producing an initial single line of contact with the adhesive so that pure rolling action ensues between the cover and back plates and the full face adhesive thereby increasing the area of contact of the full face adhesive material until the lamination is completed.
It is yet another object of the invention to provide a process in which the adhesive contact area can be driven by force by bending the glass cover and back plates sequentially in a manner to produce a rolling action.
It is also an object of the invention to provide a process wherein the adhesive contact area can be driven by force by bending the glass cover and back plate glass sequentially in a manner to produce a rolling action.
It is a still further object of the invention to produce a center-out rolling adhesive contact front lamination through a sequential annular set of vacuum chucks that can be independently moved.
It is another object of the invention to provide means to pre-align a set of display tiles to dimensions that permit automatic capture of a fiducial image on the tiles and cover and back plates.
It is a further object of the invention to provide means for dispensing the adhesives and mixing the components of the thermally curable full face adhesive.
It is still a further object of the invention to provide means to protect electronic drivers attached to the display tiles from contamination by excess adhesive.
It is also an object of the invention to provide guttering means to collect and remove excess adhesive squeezed out during the lamination process.
It is a further object of the invention to dispense adhesive in a predetermined volume over a predetermined area on an array of display tiles or on cover plates or back plates.
It is another object of the invention to optimize the lamination speed.
It is again an object of the invention to control the final thickness of adhesive between display tiles and cover and/or back plates.
It is also an object of the invention to prepare the surfaces of display tiles, cover and back plates to wet readily with adhesive to decrease the probability of trapping or forming bubbles in the adhesive.
It is a still further object of the invention to provide an adhesive having a viscosity for lamination under preferred conditions for achieving an optimal speed of lamination without trapping or including bubbles in the adhesive.
It is yet another object of the invention to provide an adhesive material and process which responds to the preferred laminate design without adversely impacting the liquid crystal cell gap.
It is also an objective of the invention to provide adhesive posts to facilitate registration of display tiles and cover and back plates that are sufficiently viscous and rigid, so that the liquid adhesive flows around the posts during lamination without destroying their ability to sustain permanent registration after curing by UV radiation.
It is a still further objective of the invention to provide pressure during the curing of the adhesive to prevent or depress bubble which would otherwise precipitate from the adhesive during the heat up cycle.